Confined to the nutshell crust of this tiny planet Earth, what solid facts do we really have about the (possibly) infinite cosmos? I'm a devout skeptic, a major minimalist when it comes to believing the latest big-picture astrophysical results. Far too often the front-page cosmological news of one year is overthrown in the next by better (or merely different) observations. Far too often interpretation and theory and wishful thinking are misrepresented as truth.

But there are a handful of relatively sure things that I'll admit concerning the large-scale structure of spacetime:

Homogeneity and isotropy --- the universe is pretty uniform, averaging over clusters of galaxies. We don't seem to be in a special location (no "center" or "edge") and there don't seem to be special preferred directions (no "up" or "north").

Uniform expansion --- everything is moving away from everything else, at a rate proportional to distance. The pace of expansion is tricky to measure, but "running the movie backwards" suggests that ~10 to ~20 billion years or so ago everything was squeezed together in an exceedingly hot and dense state.

Microwave background --- a faint glow is visible in all directions, as though something far away were radiating heat energy at a temperature of about three degrees above absolute zero. This ties in well to a hot early universe, with photons redshifted down by expansion.